1. Field of the Invention
The present invention relates to an epitaxial compound structure having a crystal structure comprising fluorite crystal on which is epitaxially grown a thin film of simple perovskite crystal having a (011) orientation, and ferroelectric devices and superconducting devices comprising the compound structure.
2. Description of the Prior Art
Crystal having a layered perovskite structure is known to have various properties, such as ferroelectricity, superconductivity and magnetism. Ferroelectric devices, superconducting devices and many other devices have been fabricated using these properties. These properties are highly dependent on the crystal orientation, with an orientation perpendicular to the [001] orientation providing the best characteristics. In the case of a ferroelectric material, for example, polarization and coercive electric field are greatest at the orientation perpendicular to [001], and in a superconducting material, current flows most readily when the crystal orientation is perpendicular to the [001] orientation. Therefore, in order to realize high-performance devices, it is desirable to make every effort to epitaxially grow thin films of layered perovskite with an orientation perpendicular to the [001].
However, a characteristic of perovskite having a layered structure is that it readily grows two-dimensionally in the (001) plane perpendicular to the [001] orientation. As a result, there is a problem in that thin films grown on the substrate grow with a (001) orientation in which the [001] orientation is perpendicular to the substrate surface, making it difficult to achieve epitaxial growth not parallel to [001], for example, perpendicular to [001] or at an incline relative to [001].
Using polycrystalline thin films instead of epitaxially grown single-crystal thin films has been proposed as a method of overcoming this problem. However, this gives rise to a fresh set of problems in that, unlike single-crystal films, in polycrystalline films the direction in which the grains grow is not uniform, and as a result, the characteristics differ from location to location. Moreover, in some cases, in addition to the target crystals, there may also be an intemixing of another crystal phase, or amorphous phase. Devices fabricated using polycrystalline film having a layered perovskite structure exhibit variations in characteristics, and make it difficult to achieve higher integration.
The present inventors conducted extensive research and experimentation relating to the use of perovskite having a layered crystalline structure to fabricate reliable, high-performance devices that are also capable of higher integration. This led to the discovery that in order to grow a crystal structure on the substrate surface that was as parallel as possible to the [001] orientation of the layered perovskite structure, it was also necessary to focus on the crystalline layer constituting the substrate. Based on further research, it was discovered that an epitaxial compound structure comprising a thin film of simple perovskite epitaxially grown with a (011) orientation on a substrate of (001) fluorite was effective, which enabled this invention to be perfected.
An object of the present invention is to provide an epitaxial compound structure that can be used as a crystalline material for fabricating reliable, high-performance devices that are also capable of higher integration, and a device using the structure.
In accordance with the present invention, there is provided an epitaxial compound structure, comprising a (001)-oriented film of fluorite crystal, and a (011)-oriented film of simple perovskite crystal grown epitaxially on the film of fluorite crystal.
The above compound structure also includes the film of fluorite crystal being a (001)-oriented film epitaxially grown on a conductive crystal. The compound structure also includes silicon as the conductive crystal.
The present invention also provides an epitaxial compound structure, comprising a (001)-oriented film of fluorite crystal, a (011)-oriented film of simple perovskite crystal grown epitaxially on the film of fluorite crystal, and a crystal film having a layered perovskite structure grown epitaxially on the film of simple perovskite crystal.
The above compound structure also includes the film of fluorite crystal being a (001)-oriented film epitaxially grown on a conductive crystal. The compound structure also includes silicon as the conductive crystal. The compound structure also includes the crystal film having a layered perovskite structure that is a ferroelectric material, a superconducting material or a magnetic material. Also included are a ferroelectric device comprising the crystal film having a layered perovskite structure that is a ferroelectric material, and a superconducting device comprising the crystal film having a layered perovskite structure that is a superconducting material.
In accordance with the present invention, by combining fluorite crystal and simple perovskite crystal, simple perovskite crystal can be epitaxially grown with a (011) orientation, enabling an epitaxial compound structure that can be used as a high-performance crystal material for fabricating reliable, high-performance devices that can be fabricated with higher integration.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the invention.